Human Overpopulation: Causes, Effects, Problems & Solutions

Human overpopulation is an issue by itself, but can also be at the core of other key environmental and social issues.

It makes sense – more people generally means more consumption (of food, water, natural resources etc.), more waste generated, and more environmental pollution issues. 

In this guide, we discuss the causes, effects, problems and potential solutions behind overpopulation.

(Note – this guide includes general information on human overpopulation, and is a ‘starter’ type resource only. It is not a definitive guide for the issue of overpopulation)


Summary – Human Overpopulation

One way to describe human overpopulation is the point at which the number of humans in an area, region, city, country, or the world at large, cannot be maintained

This might occur because there is not enough resources to support that number of humans, or because the man made systems or natural environment begin to degrade or deplete in terms of ability/capacity to support those humans [although – there is a difference between supporting a population’s basic needs, and supporting all consumer choices – which might be excessive, and/or unsustainable]

So, there can really be two parts to overpopulation that can work in conjunction with each other – 1. the size (and growth or shrinking) of the population, and, 2. how effectively and sustainably that population can be supported. 

A smaller or stagnating population could face issues if they consume at an unsustainable rate, degrade their environment at an unsustainable rate, or run out of or don’t have access to resources

The number of humans in one area at one time can increase because of a number of reasons, but some of the main reasons might include increased birth rates, decrease in the mortality/death rates, and increase in immigration

Historically, technological revolutions or advances in technologies have also increased populations e.g. the tool-making revolution, the agricultural revolution, and the industrial revolution – all of which allowed humans more access to food, resulting in subsequent population explosions

The fertility rate is said to be strongly influenced by cultural and social norms that are rather stable, and therefore slow to adapt to changes in the social, technological, or environmental conditions

Population increase rates tend to be highest in areas where children die young, where there is poverty (especially extreme poverty), and where there is lack of access to education

Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty

Guatemala is an example of a country whose average family size halved with the decrease in extreme poverty. Cambodia and Namibia are two countries who have experienced similar trends

Globally, populations in some of the poorest countries in the world are expected to double and even triple by 2040-50

Overpopulation in lower income countries might be seen as undesirable as economic development falls far behind a point where there is proper capital available to invest in the people and the country to support them. If you add mismanagement on the government level, corruption and a lack of effective social and governmental systems – problems can become worse

A quickly growing population, or a population size that is already too big, can place a strain on already depleting or stressed resources. One example of this is a city’s water supply

Over population can mean more resources are needed by a population as a whole, but also more waste is produced, and there is more pollution and environmental degradation as a flow on result. As a few examples … an increasing population might mean more water is required for food/agriculture and energy production in the future, more waste such as plastic is generated, and there is more water pollution, air pollution, soil/land pollution and general waste and environmental pollution

Economically, with overpopulation, there might be more consumers and employees/skills introduced to the economy, and the economy could grow in some ways overall, but there may also be more labor and more competition for jobs

Increasing populations aren’t always the sole cause of other social or environmental issues. One example of this is greenhouse gas emissions – they can be increased by other related or unrelated factors such as rate of economic growth and industrialisation, total consumption and consumption rate per capita, a city’s energy mix and energy carbon intensity, and how key industries such as electricity production, transport and agriculture operate 

The effects of overpopulation can be compounded by overconsumption, broken or inefficient social and governmental systems, ineffective technology, environmental pollution and degradation, and other factors

A growing population or a large population isn’t always a negative – there can be positives as well

Technology and stage of economic development can play a large role in providing enough resources for a population e.g. look at the difference between agricultural sectors in developing vs developed countries, as well as the capacity to produce electricity, provide cold food storage, and so on

But, even in developed countries and cities, there can be supply issues related to population. Perth in Western Australia is a dry city, but faces many of the same challenges as Cape Town (dry city, increasing population, prone to droughts). Perth was able to provide enough freshwater and Cape Town experienced a water shortage because of various factors like good governmental planning, investment in water treatment and recycling, investment in desalination plants and so on.

The US across many measures (along with other developed countries) consume far more resources per capita than many poorer countries, and produce more waste per capita as well

The most overpopulated cities tend to be in developing countries where poverty is rampant due to this overcrowding (leading to potential problems like sickness, disease, death and so on). Identifying overcrowded cities in underdeveloped regions, in terms of number of people per square area and income per capita, can help

Even in developed countries, heavily populated cities might deal with intense smog and pollution problems that exacerbate health and poverty issues. Labor prices can also start to diminish with an increase in labor

Solutions to overpopulation might include reducing poverty, lifting education rates, increasing the quality of health care and safety (especially for children), and investing in basic living resources for the poorest countries, or countries with the highest fertility and population increase rates

Other general solutions might include investing in technology to provide the most crucial resources for a basic standard of living for a population, becoming clear on exactly how many people each city in the world can sustainably support with the technology, resources and systems they currently have available, more education and access to healthcare for women in regards to pregnancy, more effective education for men on contraception, enforcing birth laws/regulations for the most heavily populated and quickest growing cities and countries where there’s an unsustainable increasing population or large population, and to examine our consumption and waste habits city by city. Cities might focus on quality of life as a measurement, in addition to how many people an individual city or geographic area can support (carrying capacity of a region)

Each city has it’s own capabilities and carrying capacity to support different populations to different extents – it’s too general to examine overpopulation at the country or state/province level

Some people have suggested space colonization and making use of resources in space as an additional option in the future for further human population expansion

Some experts say that science and technology alone can’t help us fix some overpopulation problems, and a cultural-social-political shift will be needed instead 

The world’s population currently sits at around 7 billion in 2019, and is forecasted to reach somewhere between 9 to 13 billion between 2050 to 2100 

Most of the world’s expected population increase [in the future] will be in Africa and Southern Asia. Africa’s population is expected to rise from the current one billion to four billion by 2100, and Asia could add another billion in the same period. [So, we might focus on these regions specifically]

Almost all growth [in future population] will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to increase to 7.8 billion in 2050. By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion. An exception is the United States population, which is expected to increase by 44% from 2008 to 2050 (

When you look at current birth rates – these forecasts make sense. The least developed regions in the world have far higher birth rates than developed regions. As the least developed countries grow their economies in the future, birth rates are expected to fall, but to still outpace the most developed countries.

A theoretical question to ask might be ‘With current technology, science, natural resources and environmental conditions – what population number can the world, and individual countries and cities sustain? What would the standard and quality of living be at that number? What factors and considerations are this number based on?’

Another theoretical question to ask might be ‘What is going to be the result of population growth at the current rate to 2050, 2100, and beyond?’

There is more information in this guide about whether humans and Earth might run out of resources in the future, and what might happen if we do


What Is Human Overpopulation?

A general definition might be:

  • Human overpopulation occurs when the ecological footprint of a human population in a specific geographical location exceeds the carrying capacity of the place occupied by that group.
  • [it usually involves the] rapid depletion of non-renewable resources or … degradation of the capacity of the environment [in the long term]



Causes of Human Overpopulation

Some of the underlying causes of overpopulation might relate to:

  • … an increase in births (fertility rate)
  • … a decline in the mortality rate
  • … an increase in immigration
  • … or an unsustainable biome and depletion of resources [for example – an unstable water supply might come from naturally dry and drought prone areas]



  • The higher the death rate for children in a region, the higher the birthrate
  • When people know their children will survive, they have few children. 



  • Poverty and the lack of access to education leads to higher birthrates and overpopulation.

– USAID, via


  • When poverty rates drop, birthrates soon follow …
  • Extreme poverty in Guatemala has decreased by nearly 40% since 1992, and with that decline in poverty, the average family size has fallen from almost 6 children to just over 3.
  • In 1994, the average family in Cambodia had nearly 6 children; by 2015, extreme poverty (living on less than $1.25 per day) in Cambodia had fallen more than 40% and average family size had decreased by more than half.
  • The last 20 years in Namibia have seen extreme poverty rates fall by 20% and average family size halved.



  • [Historically] technological revolutions [like the tool making, agricultural and industrial revolutions] have coincided with population expansion.
  • [These revolutions did things like allow humans to produce more, or get more access to more resources like food]
  • Today, starvation is caused by economic and political forces rather than a lack of the means to produce food.
  • Significant increases in human population occur whenever the birth rate exceeds the death rate for extended periods of time.
  • Traditionally, the fertility rate is strongly influenced by cultural and social norms that are rather stable and therefore slow to adapt to changes in the social, technological, or environmental conditions.
  • … improved sanitation, child immunizations, and other advances in medicine [along with stable birth rates, has lead to increased population growth in the past]
  • [More children are reaching adulthood now than in the past too – which has lead to greater population sizes]
  • There is a strong correlation between overpopulation and poverty
  • In contrast, the invention of the birth control pill and other modern methods of contraception resulted in a dramatic decline in the number of children per household in all but the very poorest countries.



  • An example of a country whose laws and norms are hindering the global effort to slow population growth is Afghanistan [which impacted women’s rights and freedoms]
  • Religious and ideological opposition to birth control has been cited as a factor contributing to overpopulation and poverty.



Effects Of Human Overpopulation

Overpopulation can mean more resources are needed by a population as a whole (more consumption of food, water, natural resources, etc.), but also more waste is produced, and there is more pollution and environmental degradation as a flow on result (air, water, and land pollution)

Some issues created (in part by), or exacerbated by an increase in population are:

Waste Pollution (including Plastic Pollution)

Water Pollution

Water Quantity & Quality Related Issues

Climate Change & Increased GHG Gas Emissions

Outdoor Air Pollution

Indoor Air Pollution

Increased Deforestation (with one of the main causes being to clear land for agriculture)

Increased Land & Soil Degradation

Decreased Biodiversity (as a result of habitat loss) – it is thought growth of human population has had more impact on biodiversity than any other single factor in the 20th century – further outlines the impact of an increasing population on wildlife and biodiversity

Food Waste & Loss

+ other issues


  • Scientists suggest that the human impact on the environment as a result of overpopulation, profligate consumption and proliferation of technology has pushed the planet into a new geological epoch known as the Anthropocene.



Specifically some of the impacts of growing populations on humans might be:

  • … spread of antibiotic resistant bacteria diseases … and new viruses that infect humans [from activities like industrial agriculture]
  • Increased chance of the emergence of new epidemics and pandemics 
  • For many environmental and social reasons, including overcrowded living conditions, malnutrition and inadequate, inaccessible, or non-existent health care, the poor are more likely to be exposed to infectious diseases.


The effects of overpopulation can be compounded by overconsumption:

  • Rich western countries are now siphoning up the planet’s resources and destroying its ecosystems at an unprecedented rate … we have triggered a major extinction event … If everyone consumed resources at the US level – which is what the world aspires to – you will need another four or five Earths.
  • We are wrecking our planet’s life support systems.



  • Resources can be unevenly distributed between the low and high income
  • There are too many people trying to fill a limited number of jobs within an area (labor price is diminished)
  • The most overpopulated cities tend to be in developing countries where poverty is rampant due to overcrowding
  • Even in developed countries, the cities listed deal with intense smog and pollution problems that exacerbate health and poverty issues.
  • In less developed regions, there is a higher death rate for children and adolescents. Unsanitary living conditions threaten survival rates. This is especially evident in urban areas where crowding is so common that slums have grown rapidly.



  • Where rapid population growth far outpaces economic development, countries will have a difficult time investing in the human capital needed to secure the well-being of its people and to stimulate further economic growth.
  • This issue is especially acute for the least developed countries, many of which are facing a doubling, or even a tripling of their populations by 2050.

– UN Population Fund, via


Potential Human Overpopulation Solutions & Strategies

Some of the major ways to address human overpopulation might be:

Solutions can be applied on different levels – individual, city, State, country, global, and so on

Have more studies into the total population a geographic area (like a city) can sustainably support

Focussing on improving overall quality of human life to a particular benchmark

Reduce poverty (in part – this involves investment, growing and diversifying the economy, and creating new jobs)

Increase the level and availability of education

Increase access to quality healthcare

Making safe and effective contraception available

Track important statistics like fertility rates, adult and child mortality rates, and immigration rates 

Keep track of environmental boundaries, and how close we are to crossing them to the point that it’s difficult or impossible to restore the environment to a sustainable state

Separate to population totals, look at other factors such as how much and how efficiently we consume, increasing the availability of renewable natural resources, and so on. It’s possible that changes in lifestyle and changes in available resources could support further population growth


  • Changes in lifestyle could reverse overpopulated status without a large population reduction.



  • Addressing global poverty and keeping children alive is crucial for reducing overpopulation.



  • The key thing you can do to reduce population growth is actually improve health.

– Bill Gates, via


  • In order to combat poverty [and help ensure children are surviving into adulthood] in the most overpopulated cities, education and economic growth are critical.
  • [This will also help overcome] environmental pollution



Proposed solutions and ways to mitigate overpopulation related issues according to are:

  • [Looking at] social, cultural, behavioral and political norms …
  • … put policies in place that regulate the number of children allowed to a couple [China has done this. This leads to smaller families – making it a social norm in all countries to have small families]
  • … [make] it easier and more socially acceptable to use safe contraception and birth control methods, with safe abortion as a backup. Worldwide, nearly 40% of pregnancies are unintended (some 80 million unintended pregnancies each year. In poorer countries, women have unplanned pregnancies, and might like to be able to space out their pregnancies more. More awareness on family planning can also help
  • Where women [are put in control of their reproductive rights] birth rates fall. [Female education and women in the work force can also help]
  • Scientists and technologists … caution that science and technology, as currently practiced, cannot solve the serious problems global human society faces, and that a cultural-social-political shift is needed to reorient science and technology in a more socially responsible and environmentally sustainable direction.
  • [cultural and religious beliefs of community members in a country can influence birth rates]
  • [Forced sterilization has been tried in countries such as India before]
  • [Choice-based, marketable birth license plans are also an option] where the market would determine what the license fee for each additional child would cost [beyond a certain pre determined population growth goal]
  • Space Expansion … Extraterrestrial settlement & space colonisation is also a potential solution to explore. [Some sources indicate the] resources of the solar system could support 10 quadrillion (1016) people. But, other sources argue it is not viable to address Earth overpopulation by expanding to Space
  • Urbanisation …
  • … urbanization may be the best compromise in the face of global population growth … [and it might happen if] urban planning is significantly improved and city services are properly maintained.



  • [SA provides stats on women without effective modern contraception, and unintended pregnancies and abortions]
  • In every nation … in which a choice of contraceptives is available and is backed up by reasonably accessible safe abortion for when contraception fails, women have two or fewer children.
  • Educating girls reduces birthrates, as well as women enter the workforce, starting businesses, inheriting assets and otherwise interacting with men on an equal footing, their desire for more than a couple of children fades even more dramatically.
  • Most of the drop in Chinese fertility occurred … as the government brought women by the millions into farm and industry collectives and provided them with the family planning they needed to stay on the job.
  • Many developing countries—from Thailand and Colombia to Iran—have experienced comparable declines in family size by getting better family-planning services and educational opportunities to more women and girls in more places.



Top 20 Countries With Largest Populations In Total People

As of September 2018, these are the top 20 largest population countries:

  1. China – 1,416,221,148
  2. India –  1,357,226,853
  3. USA – 327,258,161
  4. Indonesia – 267,393,413
  5. Brazil – 211,204,519
  6. Pakistan – 201,628,675
  7. Nigeria – 196,949,995
  8. Bangladesh – 166,730,612
  9. Russia – 143,959,398
  10. Mexico – 131,100,059
  11. Japan – 127,121,981
  12. Ethiopia – 108,089,628
  13. Phillipines  – 106,853,251
  14. Egypt – 99,766,661
  15. Vietnam – 96,693,923
  16. Democratic Republic Of The Congo – 84,581,357
  17. Germany – 82,331,523
  18. Iran – 82,192,940
  19. Turkey  – 82,167,606
  20. Thailand – 69,214,108



In addition to countries, we might also look at the cities with the largest populations, and match them up with cities with the lowest average incomes, and lowest quality of life.


Past, Current & Future World Population Stats & Forecasts/Projections, Including Population Growth

You can see past, current and future world population stats and forecasts here:

  • – countries with biggest population by 2060
  • – most populous cities by 2100


  • The world’s population will rise from just over 7 billion in 2012 to nearly 9.6 billion by 2050



  • The world population is currently growing by approximately 74 million people per year. Current United Nations predictions estimate that the world population will reach 9.0 billion around 2050, assuming a decrease in average fertility rate from 2.5 down to 2.0.
  • Almost all growth will take place in the less developed regions, where today’s 5.3 billion population of underdeveloped countries is expected to increase to 7.8 billion in 2050. By contrast, the population of the more developed regions will remain mostly unchanged, at 1.2 billion. An exception is the United States population, which is expected to increase by 44% from 2008 to 2050.



Fertility Rates, & Replacement Level Rates

  • “Replacement level fertility” is the total fertility rate—the average number of children born per woman—at which a population exactly replaces itself from one generation to the next, without migration.
  • This rate is roughly 2.1 children per woman for most countries, although it may modestly vary with mortality rates.
  • Sub-Saharan Africa is the exception to this fertility trend. Its total fertility rate was 5.4 during the 2005–10 period― double that of any other region―and is projected to decline only to 3.2 by 2050.
  • These expected reductions in fertility rates reflect expectations of increasing urbanization, expected declines in child mortality, and increases in income, among other factors.



The birth rates by country development level are:

  • World – 2.5
  • More Developed – 1.7
  • Less Developed – 2.6
  • Least Developed – 4.3

– UNFPA, via


Carrying Capacity

  • Carrying capacity refers to the number of individuals who can be supported in a given area within natural resource limits, and without degrading the natural social, cultural and economic environment for present and future generations. The carrying capacity for any given area is not fixed.
  • It can be altered by improved technology, but mostly it is changed for the worse by pressures which accompany a population increase.
  • As the environment is degraded, carrying capacity actually shrinks, leaving the environment no longer able to support even the number of people who could formerly have lived in the area on a sustainable basis.
  • No population can live beyond the environment’s carrying capacity for very long.
  • We must think in terms of “carrying capacity” not land area.



  • A world population of around a billion would have an overall pro-life effect.
  • This could be supported for many millennia and sustain many more human lives in the long term compared with our current uncontrolled growth and prospect of sudden collapse



Countries With The Worst Human, Wildlife & Environmental Issues

Rather than looking at overall population numbers – instead, we might look at whether the population has enough resources to meet demand, look at quality of life indicators (such as homelessness and access to certain basic opportunities and services), and look at population effect on humans, wildlife and the environment. We may also look at economic factors like unemployment, and income levels. These things can be indicators and benchmarks of how sustainable or unsustainable a population size is.

Also look at human density (also called overcrowding) – number of people per square mile in that city.


10 of the most overcrowded cities in the world in 2017 based on number of people per square mile are:

  • 1. Dhaka, Bangladesh – 16,235,000 total people, and 114,300 per square mile
  • 2. Hyderabad, Pakistan – 2,990,000 total people, and 106,800 per square mile
  • 3. Vijayawada, India – 1,775,000 total people, and 80,700 per square mile
  • 4. Chittagong, Bangladesh –  3,250,000 total people, and 75,600 per square mile
  • 5. Mumbai, India – 22,885,000 total people, and 67,300 per square mile
  • 6. Hong Kong, – 7,280,000 total people, and 66,200 per square mile
  • 7. Aligarh, India – 1,050,000 total people, and 65,600 per square mile
  • 8. Macau – 655,000 total people, and 65,500 per square mile
  • 9. Hama, Syria – 1,300,000 total people, and 65,000 per square mile
  • 10. Mogadishu, Somalia – 2,265,000 total people, and 64,700 per square mile



There is also a list of the fastest growing cities in the world –


Overpopulation In Developing vs Developed Countries

It’s quite clear from the above information that overpopulation occurs at different rates, and has different results in developing vs developed countries.


An interesting stat on the future of population growth in low income countries is:

  • The UN projects the population of the 48 poorest countries in the world will double from 850 million in 2010 to 1.7 billion in 2050.

Population Institute, via the












10. – most populous cities by 2100







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